1. Field of the Invention
The invention relates to curable organic-inorganic hybrid compositions having a high refractive index, methods of making and using such compositions, and polymeric materials and articles made from such compositions. The compositions of the present invention are useful in the field of fiber optic communications.
2. Description of Related Art
For many optical applications, high refractive index materials are desirable. Inorganic glasses and crystals, such as, for example, silicon nitride and lead borosilicate glasses, while high in refractive index, are difficult to process. For example, it is difficult and/or expensive to make planar waveguides from such materials. Polymers have recently drawn attention as a material for the low-cost fabrication of devices for optical communications. Standard optical polymers have a refractive index of between about 1.30 and about 1.60 at 1550 nm. For many applications, such as, for example, the liquid crystal cross-connect switch described in commonly owned and copending U.S. patent application Ser. No. 09/431,430, which is incorporated herein by reference, these refractive indices are simply too low.
Many efforts have been made to develop high refractive index organic-inorganic hybrid materials through the use of the sol-gel process. The inorganic
species in these materials are, for example, titanium dioxide or zirconium dioxide. Although these hybrid materials are theoretically advantageous because of the high index, optical clarity and hardness of the inorganic portion, the sol-gel process can result in materials with a high hydroxyl content. The hydroxide functional group has a strong vibrational overtone at around 1550 nm. Thus, in order to be useful in optical communications, sol-gel derived materials must be substantially dehydroxylated. However, the process of conventional dehydroxylation, requires a high temperature treatment and can damage the organic portion of the material, and can create cracking problems in films thicker than five microns and in monolithic materials. This cracking is due to high capillary pressure and the stress induced by shrinkage from the removal of water and alcohol through condensation reactions and evaporation. Further, the shrinkage of these materials makes them unsuitable for use in polymer microreplication processes.
Another method for the incorporation of inorganics into processable polymer materials is the dispersion of pulverized titania particles in a resin binder. One disadvantage of this method is the aggregation and/or agglomeration of particles due to the hydrophilicity of the surfaces of the particles.
One aspect of the present invention relates to an energy curable composition including condensed high refractive index metal oxide nanoparticles; a high refractive index organometallic coupling agent; an energy curable organometallic coupling agent including an energy curable organic moiety; and a high refractive index energy curable monomer or oligomer.
Another aspect of the present invention relates to an energy curable composition wherein the high refractive index organometallic coupling agent has the formula RcxRyMQ4-x-y where M is a metal atom selected from the group consisting of Si, Ti, Zr, and Sn, Rc is an organic moiety with a refractive index of at least about 1.52 at 1550 nm bound to the metal atom by a carbon atom, R is an organic moiety bound to the silicon atom by a carbon atom, Q is a hydrolyzable ligand selected from the group consisting of chlorine, bromine, iodine, alkoxy, and acyloxy, x is 1, 2, or 3, y is 0, 1, or 2, and the sum of x and y is no greater than 3; and the energy curable organometallic coupling agent including an energy curable organic moiety has the formula RdxRyMQ4-x-y wherein M is a metal atom selected from the group consisting of Si, Ti, Zr, and Sn, Rd is an organic moiety including an energy curable functional group, R is an organic moiety bound to the metal atom by a carbon atom, Q is a hydrolyzable ligand selected from the group consisting of chlorine, bromine, iodine, alkoxy, and acyloxy, x is 1, 2, or 3, y is 0, 1, or 2, and the sum of x and y is no greater than 3.
Another aspect of the present invention relates to a polymeric material including condensed metal oxide nanoparticles having a mixture of organometallic coupling agents covalently bound to the exterior surface of the nanoparticles; and a high refractive index solid polymer matrix, wherein the mixture of organometallic coupling agents includes a high refractive index organometallic coupling agent, and an organometallic coupling agent covalently bound to the polymer matrix; and the condensed metal oxide nanoparticles are homogeneously dispersed in the solid polymer matrix.
Another aspect of the present invention relates to a planar optical device having a waveguide core and a waveguide cladding, wherein at least one of the waveguide core and waveguide cladding are made from the polymeric material of the present invention.
Another aspect of the present invention relates to a thin film optical device having alternating layers of transparent materials with differing refractive indices, wherein at least one of the materials is the polymeric material of the present invention.
Another aspect of the present invention relates to a monolithic optical element including the polymeric material of the present invention.
Another aspect of the present invention relates to a process for making an energy curable composition by reacting condensed metal oxide nanoparticles with a mixture of a high refractive index organometallic coupling agent and an organometallic coupling agent containing an energy curable organic moiety to yield nanoparticles with the mixture of the coupling agents covalently bound to the surface of the nanoparticles; and dispersing the nanoparticles so formed in at least one high refractive index energy curable monomer or oligomer.
Another aspect of the present invention relates to a process for making a polymeric material by reacting condensed metal oxide nanoparticles with a mixture of a high refractive index organometallic coupling agent and an organometallic coupling agent containing an energy curable organic moiety to yield nanoparticles with the mixture of the coupling agents covalently bound to the surface of the nanoparticles; dispersing the nanoparticles so formed in at least one high refractive index energy curable monomer or oligomer; and curing the composition so formed with a source of energy.
Another aspect of the present invention is a process for making an article of manufacture comprising the steps of reacting condensed metal oxide nanoparticles with a high refractive index organometallic coupling agent and an organometallic coupling agent containing an energy curable organic moiety to yield nanoparticles with the coupling agent or agents bound to the surface of the nanoparticles; dispersing the mixture so formed in at least one high refractive index energy curable monomer or oligomer; contacting the composition so formed with a mold surface; curing the composition in contact with the mold with a source of energy; and removing the article so formed from the mold surface.
The materials of the present invention have a high refractive index in the infrared, above about 1.60 at 1550 nm, making them suitable for use in certain devices for optical communication, such as a liquid crystal cross-connect device. Low shrinkage upon cure is observed, and low coefficient of thermal expansion, low thermo-optic coefficient and low birefringence of the polymeric material are expected due to the high inorganic content of these materials. The materials of the present invention may be formulated to have lower optical loss than their wholly organic counterparts due to lower optical loss of the inorganic constituents. The energy curable composition has good wettability, and the polymeric material has good release characteristics from nickel microreplication tools as well as good adhesion to silaceous substrates such as glass, silica, and silicon, making the materials of this invention well suited for use in polymer microreplication processes.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the written description or recognized by practicing the invention as described in the written description and claims hereof, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework to understanding the nature and character of the invention as it is claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s) of the invention, and together with the description serve to explain the principles and operation of the invention.